feat(postgres): use standard Unix socket directory if host is omitted

sqlx-postgres/src/options/doc.md

@@ -60,6 +60,7 @@ postgresql://user@localhost
 postgresql://user:secret@localhost
 postgresql://user:correct%20horse%20battery%20staple@localhost
 postgresql://localhost?dbname=mydb&user=postgres&password=postgres
+postgresql:///mydb
 ```
 
 See also [Note: Unix Domain Sockets](#note-unix-domain-sockets) below.
@@ -106,8 +107,9 @@ This behavior is _only_ implemented for the environment variables, not the URL p
 Note: passing the SSL private key via environment variable may be a security risk.
 
 # Note: Unix Domain Sockets
-If you want to connect to Postgres over a Unix domain socket, you can pass the path
-to the _directory_ containing the socket as the `host` parameter.
+If you want to connect to Postgres over a Unix domain socket, you can either pass the path
+to the _directory_ containing the socket as the `host` parameter, or leave the host part of the URL empty.
+When the host part is omitted, the standard Unix socket directory is used.
 
 The final path to the socket will be `{host}/.s.PGSQL.{port}` as is standard for Postgres.
 

sqlx-postgres/src/options/mod.rs

@@ -62,7 +62,9 @@ impl PgConnectOptions {
         let host = var("PGHOSTADDR")
             .ok()
             .or_else(|| var("PGHOST").ok())
-            .unwrap_or_else(|| default_host(port));
+            .unwrap_or_else(|| "localhost".into());
+
+        let socket = default_socket(port);
 
         let username = var("PGUSER").ok().unwrap_or_else(whoami::username);
 
@@ -71,7 +73,7 @@ impl PgConnectOptions {
         PgConnectOptions {
             port,
             host,
-            socket: None,
+            socket,
             username,
             password: var("PGPASSWORD").ok(),
             database,
@@ -575,7 +577,7 @@ impl PgConnectOptions {
     }
 }
 
-fn default_host(port: u16) -> String {
+fn default_socket(port: u16) -> Option<PathBuf> {
     // try to check for the existence of a unix socket and uses that
     let socket = format!(".s.PGSQL.{port}");
     let candidates = [
@@ -586,12 +588,11 @@ fn default_host(port: u16) -> String {
 
     for candidate in &candidates {
         if Path::new(candidate).join(&socket).exists() {
-            return candidate.to_string();
+            return Some(PathBuf::from(candidate));
         }
     }
 
-    // fallback to localhost if no socket was found
-    "localhost".to_owned()
+    None
 }
 
 /// Writer that escapes passed-in PostgreSQL options.

sqlx-postgres/src/options/parse.rs

@@ -273,6 +273,26 @@ fn it_parses_socket_correctly_percent_encoded() {
 
     assert_eq!(Some("/var/lib/postgres/".into()), opts.socket);
 }
+
+#[test]
+fn it_uses_default_socket_if_host_is_skipped() {
+    let path_to_socket = format!("{}/.s.PGSQL.5432", default_socket_dir());
+    let _ = std::fs::File::create(&path_to_socket)
+        .unwrap_or_else(|e| panic!("error while creating tmp socket file: {}", e));
+
+    let url = "postgresql:///database";
+    let opts = PgConnectOptions::from_str(url).unwrap();
+
+    let _ = std::fs::remove_file(&path_to_socket)
+        .unwrap_or_else(|e| panic!("error while deleting tmp socket file: {}", e));
+
+    assert_eq!(
+        Some(std::path::PathBuf::from(default_socket_dir())),
+        opts.socket
+    );
+    assert_eq!(Some("database".into()), opts.database);
+}
+
 #[test]
 fn it_parses_socket_correctly_with_username_percent_encoded() {
     let url = "postgres://some_user@%2Fvar%2Flib%2Fpostgres/database";
@@ -318,6 +338,48 @@ fn it_returns_the_parsed_url_when_socket() {
     assert_eq!(expected_url, opts.build_url());
 }
 
+#[test]
+fn it_returns_the_parsed_url_with_default_socket_when_host_is_not_defined() {
+    let port = 5432;
+    let path_to_socket =
+        std::path::PathBuf::from(format!("{}/.s.PGSQL.{}", default_socket_dir(), port));
+
+    let _ = std::fs::File::create(&path_to_socket)
+        .unwrap_or_else(|e| panic!("error while creating tmp socket file: {}", e));
+
+    let url = "postgresql:///database";
+    let opts = PgConnectOptions::from_str(url).unwrap();
+
+    let _ = std::fs::remove_file(&path_to_socket)
+        .unwrap_or_else(|e| panic!("error while deleting tmp socket file: {}", e));
+
+    let encoded_socket = utf8_percent_encode(&default_socket_dir(), NON_ALPHANUMERIC).to_string();
+    let encoded_url = format!(
+        "postgres://{}@{}/database",
+        whoami::username(),
+        encoded_socket
+    );
+    let mut expected_url = Url::parse(&encoded_url).unwrap();
+    // PgConnectOptions defaults
+    let query_string = "sslmode=prefer&statement-cache-capacity=100";
+    expected_url.set_query(Some(query_string));
+    let _ = expected_url.set_port(Some(port));
+
+    assert_eq!(expected_url, opts.build_url());
+}
+
+#[cfg(test)]
+fn default_socket_dir() -> String {
+    #[cfg(target_os = "macos")]
+    {
+        "/private/tmp".into()
+    }
+    #[cfg(target_os = "linux")]
+    {
+        "/tmp".into()
+    }
+}
+
 #[test]
 fn it_returns_the_parsed_url_when_host() {
     let url = "postgres://username:p@ssw0rd@hostname:5432/database";